The food and beverage industries principally employ the enzyme, .beta.-amylase (EC 3.2.1.1.2), to convert starch into maltose solutions. .beta.-Amylase hydrolyzes the .alpha.-1,4-glucosidic linkages in an exo-fashion from the non-reducing end of starch-type subtrates, and produces both maltose in the .beta.-anomeric configuration and .beta.-limit dextrins from starch. The .beta.-amylase employed in most industrial applications is obtained from plants. Attempts have been made to obtain a more active, thermostable and extracellular enzyme from microorganisms. However, the known microbial .beta.-amylases are not active or thermostable enough to substitute for the plant enzyme. Therefore, the plant .beta.-amylases continue to be used for maltose production although they are expensive and relatively unstable.
Only a few enzymes of current industrial interest have been isolated and characterized from thermoanaerobes. The thermostable and active enzymes characterized to date from thermoanaerobes, include an endoglucanase of Clostridium thermocellum, an alcohol dehydrogenase of Thermoanaerobium brockii and C. thermohydrosulfuricum and a polygalacturonate hydrolyase of C. thermosulfurogenes (1,2). It would obviously be desirable to have a more thermostable .beta.-amylase than those currently available.